In telephone communications involving d-c pulse signalling, it is known to provide pulse rejection circuitry which prevents unwanted spikes or disturbances on the line from erroneously being accepted as dial pulses. An example of such a circuit is shown in applicants' U.S. Pat. No. 3,822,385 entitled "Pulse Rejection Circuit" issued July 2, 1974 and invented by Inanc Kayalioglu.
In addition, pulse duration correction circuits which are responsive to incoming dial pulses, are also utilized to provide output pulses of a standardized or fixed time duration. Such a circuit is shown in U.S. Pat. No. 4,071,781 entitled "Pulse Duration Correction Circuit" issued Jan. 31, 1978, also invented by Inanc Kayalioglu.
In some applications it may be advantageous to exercise independent control over the delay intervals and the threshold levels for both the positive and negative going portions of these pulse signals, particularly when the make-break interval of the pulses is asymmetrical as is normally the case with dial pulses.